Assay for methylation in the GST-Pi gene

ABSTRACT

A diagnostic or prognostic assay is disclosed for a disease of condition characterized by abnormal methylation of cytosine at side or sites within the glutathione-S-transferase (GST) Pi gene and/or its regulatory flanking sequences (e.g., prostate cancer and liver cancer). The assay comprises: (i) isolating DNA from said subject, and (ii) determining (e.g., by selective PCR amplification) the presence of abnormal methylation of cytosine at a site or sites within the GST-Pi gene and/or its regulatory flanking sequences.

This is a divisional of application Ser. No. 09/673,448 filed Nov. 27,2000, which is a National Stage of PCT Application No. PCT/AU99/00306filed Apr. 23, 1999. The entire disclosure of Application Number09/673,448 is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to an assay for diagnosis or prognosis of adisease or condition characterised by abnormal methylation of cytosineat a site or sites within the glutathione-S-transferase (GST) Pi geneand/or its regulatory flanking sequences. In one particular application,the invention provides an assay for the diagnosis or prognosis ofprostate cancer.

BACKGROUND OF THE INVENTION

DNA Methylation in Mammalian Genomes

The only established post-synthetic modification of DNA in higher animaland plant genomes is methylation of the 5′ position of cytosine. Theproportion of cytosines which are methylated can vary from a few percentin sonic animal genomes (1) to 30% in some plant genomes (2). Much ofthis methylation is found at CpG sites where the symmetricallypositioned cytosines on each strand are methylated. In plant genomes,similar symmetrical methylation of cytosines at CpNpG (where N can beany base) is also common (3). Such sites of methylation have also beenidentified at low frequency in mammalian DNA (4).

Methylation patterns are heritable as the methylase enzyme recognises asa substrate, sites where a CpG dinucleotide is methylated on one strandbut the corresponding C on the other strand is unmethylated, andproceeds to methylase it (5, 6). Fully unmethylated sites do notnormally act as substrates for the enzyme and hence remain unmethylatedthrough successive cell divisions. Thus, in the absence of errors orspecific intervening events, the methylase enzyme enables the stableheritability of methylation patterns.

Extensive studies of gene expression in vertebrates have shown a strongcorrelation between methylation of regulatory regions of genes and theirlack of expression (7). Most of such studies have examined only alimited number of restriction enzyme sites using enzymes which fail tocut if their target sites are methylated. A far more limited number havebeen examined at all cytosine bases using genomic sequencing methods (8,9).

Bisulphite Conversion of DNA

Treatment of single-stranded DNA with high concentrations of bisulphitefollowed by alkali leads to the selective deamination of cytosine,converting it to uracil (10, 11). By contrast, 5-methyl cytosines (5meC)are resistant to this chemical deamination. When bisulphite-treated DNAis copied by DNA polymerases, the uracils are read as if they werethymines and an adenine nucleotide incorporated, while 5meC is stillread as a cytosine (a G being incorporated opposite). Thus, after aregion of sequence is amplified by polymerase chain reaction (PCR),cytosines in the sequence which were methylated in the original DNA willbe read as cytosines while unmethylated cytosines will be read asthymines (12, 13).

PCR Amplification of Methylated and Unmethylated DNA

In order to amplify bisulphite-treated DNA, primers are designed toanneal to the sequence produced after bisulphite treatment of the DNA.Since cytosines are converted to uracils, the base in the annealingprimer will be an adenine rather than a guanine for the non-convertedcytosine. Similarly, for the other primer of the pair, thymines replacecytosines. To permit quantification of levels of methylation in thetarget DNA, primers are normally chosen to avoid sites which may or maynot be methylated (particularly CpG sites) and so may contain either a5meC or a uracil after bisulphite treatment. Use of such non-selectiveprimers allows both methylated and unmethylated DNAs to be amplified byPCR, providing for quantification of the level of methylation in thestarting DNA population. The PCR-amplified DNA can be cut with aninformative restriction enzyme, can be sequenced directly to provide anaverage measure of the proportion of methylation at any position ormolecules may be cloned and sequenced (each clone will be derived fromamplification of an individual strand in the initial DNA). Such studieshave indicated that, while a population of molecules may conform to anoverall pattern of methylation, not all molecules will be identical andmethylation may be found on only a fraction of molecules at some sites(13, 16).

Selective Amplification of Methylated DNA

Recently Herman et al. (14) described a variation of the bisulphitesequencing procedure to make it selective for the amplification of onlymethylated DNA. In this work, PCR primers were used which were designedto discriminate between the sequences produced afterbisulphite-treatment of methylated and non-methylated target DNAs. Thus,cytosines which formed part of a CpG site would not be bisulphiteconverted and would remain as cytosines in the methylated DNA but wouldbe converted to uracils in the unmethylated target DNA; Primersutilising these differences were designed and used for the amplificationof methylated DNA sequences from four tumour suppressor genes, p16, p15,E-cadherin and von Hippel-Lindau.

Methylation of the Glutathione-S-Transferase Pi Gene in Prostate Cancer

Lee et al. (15) (U.S. Pat. No. 5,552,277 and International PatentApplication No PCT/US95/09050) demonstrated that expression of theglutathione-S-transferase (GST) Pi gene is lost in nearly all cases ofprostate cancer. They further showed that in twenty cases examined,using Southern blotting, that this loss of expression was accompanied bymethylation at a specific restriction enzyme site (BssHII) in thepromoter region of the gene. This methylation was not seen in normalprostate tissue or in a number of other normal tissues examined. Inexamining a prostate cancer cell line in which the GST-Pi gene isinactive, they also identified methylation at two other restrictionenzyme sites, NotI and SacII in the promoter region of the gene.Digestion of cell line DNAs with the enzymes MspI and HpaII, indicatedthat the correlation of DNA methylation with lack of expression was notmaintained for these sites which were largely located downstream of thetranscription start site. The nature of the data makes it difficult toreach conclusions on the methylation status of individual MspI/HpaIIsites. However, Lee et al. (18) were able to show that following HpaIIdigestion (which will cut at all unmethylated HpaII sites), a region ofDNA containing twelve HpaII recognition sites could be amplified by PCRfrom tumour DNA, but not from normal prostate or leukocyte DNA. Thisindicates that some DNA molecules in prostate cancer are methylated atall these HpaII sites, while DNAs from normal prostate and leukocyte DNAmust contain at least one of these sites unmethylated (as a single cutwill render the region incapable of being amplified by PCR).

The present inventors have identified and developed an alternativemethod for detecting sites of methylation present in DNA from prostatecancer tissue but not present in DNA from normal tissue. The methodrelies on selective amplification of a target region of the GST-Pi genebut does not require prior restriction with an informative restrictionenzyme.

DISCLOSURE OF THE INVENTION

Thus, in a first aspect, the present invention provides a diagnostic orprognostic assay for a disease or condition in a subject, said diseaseor condition characterised by abnormal methylation of cytosine at a siteor sites within the glutathione-S-transferase (GST) Pi gene and/or itsregulatory flanking sequences, wherein said assay comprises the stepsof;

-   (i) isolating DNA from said subject,-   (ii) exposing said isolated DNA to reactants and conditions for the    amplification of a target region of the GST-Pi gene and/or its    regulatory flanking sequences which includes a site or sites at    which abnormal cytosine methylation characteristic of the disease or    condition occurs, the amplification being selective in that it only    amplifies the target region if the said site or sites at which    abnormal cytosine methylation occurs is/ale methylated, and-   (iii) determining the presence of amplified DNA,    wherein the amplifying step (ii) is used to amplify a target region    of the GST-Pi gene and/or its regulatory flanking sequences defined    by (and inclusive of) CpG sites −43 to +55.

Since the amplification is designed to only amplify the target region ifthe said site or sites at which abnormal cytosine methylation (i.e. ascompared to the corresponding site or sites of DNA from subjects withoutthe disease- or condition being assayed) occurs is/are methylated, thepresence of amplified DNA will be indicative of the disease or conditionin the subject from which the isolated DNA has been obtained. The assaythereby provides a means for diagnosing or prognosing the disease orcondition in a subject.

The step of isolating DNA may be conducted in accordance with standardprotocols. The DNA may be isolated from any suitable body sample, suchas cells from tissue (fresh or fixed samples), blood (including serumand plasma), semen, urine, lymph or bone marrow. For some types of bodysamples, particularly fluid samples such as blood, semen, urine andlymph, it may be preferred to firstly subject the sample to a process toenrich the concentration of a certain cell type (e.g. prostate cells).One suitable process for enrichment involves the separation of requiredcells through the use of cell-specific antibodies coupled to magneticbeads and a magnetic cell separation device.

Prior to the amplifying step, the isolated DNA is preferably treatedsuch that unmethylated cytosines are converted to uracil or anothernucleotide capable of forming a base pair with adenine while methylatedcytosines are unchanged or are converted to a nucleotide capable offorming a base pair with guanine. This treatment permits the design ofprimers which enable the selective amplification of the target region ifthe said site or sites at which abnormal cytosine methylation occursis/are menthylated.

Preferably, following treatment and amplification of the isolated DNA, atest is performed to verify that unmethylated cytosines have beenefficiently converted to uracil or another nucleotide capable of forminga base pair with adenine, and that methylated cystosines have remainedunchanged or efficiently converted to another nucleotide capable offorming a base pair with guanine.

Preferably, the treatment of the isolated DNA involves reacting theisolated DNA with bisulphite in accordance with standard protocols. Aswill be clear from the above discussion of bisulphite treatment,unmethylated cytosines will be converted to uracil whereas methylatedcytosines will be unchanged. Verification that unmethylated cytosineshave been converted to uracil and that methylated cystosines haveremained unchanged may be achieved by;

-   (i) restricting an aliquot of the treated and amplified DNA with a    suitable restriction enzyme(s) which recognise a restriction site(s)    generated by or resistant to the bisulphite treatment, and-   (ii) assessing the restriction fragment pattern by electrophoresis.    Alternatively, verification may be achieved by differential    hybridisation using specific oligonlucleotides targeted to regions    of the treated DNA where unmethylated cytosines would have been    converted to uracil and methylated cytosines would have remained    unchanged.

The amplifying step may involve polymerase chain reaction (PCR)amplification, ligase chain reaction amplification (20) and others (21).

Preferably, the amplifying step is conducted in accordance with standardprotocols for PCR amplification, in which case, the reactants willtypically be suitable primers, dNTPs and a thermostable DNA polymerase,and the conditions will be cycles of varying temperatures and durationsto effect alternating denaturation of strand duplexes, annealing ofprimers (e.g. under high stringency conditions) and subsequent DNAsynthesis.

To achieve selective PCR amplification with bisulphite-treated DNA,primers and conditions may be used to discriminate between a targetregion including a site or sites of abnormal cytosine methylation and atarget region where there is no site or sites of abnormal cytosinemethylation. Thus, for amplification only of a target region where thesaid site or sites at which abnormal cytosine methylation occurs is/aremethylated, the primers used to anneal to the bisulphite-treated DNA(i.e. reverse primers) will include a guanine nucleotide(s) at a site(s)at which it will form a base pair with a methylated cytosine(s). Suchprimers will form a mismatch if the target region in the isolated DNAhas unmethylated cytosine nucleotide(s) (which would have been convertedto uracil by the bisulphite treatment) at the site or sites at whichabnormal cytosine methylation occurs. The primers used for annealing tothe opposite strand (i.e. the forward primers) will include a cytosinenucleotide(s) at any site(s) corresponding to site(s) of methylatedcytosine in the bisulphite-treated DNA.

Preferably, the primers used for the PCR amplification are of 12 to 30nucleotides in length and are designed to anneal to a sequence withinthe target region that includes two to four cytosine nucleotides thatare abnormally methylated in the DNA of a subject with the disease orcondition being assayed. In addition, the primers preferably include aterminal nucleotide that will form a base pair with a cytosinenucleotide (reverse primer), or the guanine nucleotide opposite (forwardprimer), that is abnormally methylated in the DNA of a subject with thedisease or condition being assayed.

The step of amplifying is used to amplify a target region within theGST-Pi gene and/or its regulatory flanking sequences. The regulatoryflanking sequences may be regarded as the flanking sequences 5′ and 3′of the GST-Pi gene which include the elements that regulate, eitheralone or in combination with another like element, expression of theGST-Pi gene.

In particular, the step of amplifying is used to amplify a target regionwithin the region of the GST-Pi gene and its regulatory flankingsequences defined by (and inclusive of) CpG sites −43 to +55 (whereinthe numbering of the CpG sites is relative to the transcription startsite). The numbering and position of CpG sites is shown in FIG. 1.

The step of determining the presence of amplified DNA may be conductedin accordance with standard protocols. One convenient method involvesvisualisation of a band(s) corresponding to amplified DNA, following gelelectrophoresis.

Preferably, the disease or condition to be assayed is selected fromcancers, especially hormone dependent cancers such as prostate cancer,breast cancer and cervical cancer, and liver cancer.

For the diagnosis or prognosis of prostate cancer, the step ofamplifying preferably amplifies a target region within the region of theGST-Pi gene and its regulatory flanking sequences defined by (andinclusive of CpG sites −43 to +53, more preferably, −43 to +10. However,within these target regions it is believed that there are CpG siteswhich show variability in methylation status in prostate cancer or aremethylated in other tissues. Thus, for the target region defined by (andinclusive of) CpG sites −43 to +10, it is preferred that the primersused for amplification be designed so as to minimise (i.e. by use ofredundant primers or by avoidance of the sites) the influence of CpGsites −36, −32, −23, −20, −19, −14 and a polymorphic region coveringsite −33. Further, for DNA isolated from cells other than from prostatetissue (e.g. blood), it is preferred that the primers used be designatedto amplify a target region that does not include the region of theGST-Pi gene and its regulatory flanking sequences defined by (andinclusive on CpG sites −7 to +7, or, more preferably, −13 to +8, sincethis may lead to false positives. Further preferred target regions,therefore, are within the region of the GST-Pi gene and its regulatoryflanking sequences defined by (and inclusive of) CpG sites −43 to −14,−43 to −8, +9 to +53 and +1 to +53.

Suitable primer pairs for the diagnosis or prognosis of prostate cancer,include those consisting of a forward and reverse primer selected fromeach of the following groups: Forward Primers (i.e. anneal to the 5′ endof the target region) CGCGAGGTTTTGGTTGGAGTTTCGTCGTC (SEQ ID NO: 1)CGTTATTAGTGAGTACGCGCGGTTC (SEQ ID NO: 2) YGGTTTTAGGGAATTTTTTTTCGC (SEQID NO: 3) YGGYGYGTTAGTTYGTTGYGTATATTTC (SEQ ID NO: 4)GGGAATTTTTTTTCGCCATGTTTYGGCGC (SEQ ID NO: 5) TTTTTAGGGGGTTYGGAGCGTTTC(SEQ ID NO: 6) GGTAGGTTGYGTTTATCGC (SEQ ID NO: 7) Reverse Primers (i.e.anneal to the extension of the forward primer) TCCCATCCCTCCCCGAAACGCTCCG(SEQ ID NO: 8) GAAACGCTCCGAACCCCCTAAAAACCGCTAACG (SEQ ID NO: 9)CRCCCTAAAATCCCCRAAATCRCCGCG (SEQ ID NO: 10)ACGCCRACRACCRCTACACCCCRAAGGTCG (SEQ ID NO: 11)CTGTTCTAAAAAATCCCRCRAACTCCCGCGG (SEQ ID NO: 12)AAAACRCCGTAAAATGGGCGAAATCGCCG (SEQ ID NO: 13)AACTCCGRCCGACGCCAACGCCGACGACCG (SEQ ID NO: 14)AAAAATTCRAATCTCTCCGAATAAACG (SEQ ID NO: 15) AAAAACCRAAATAAAAACCAGACGACG(SEQ ID NO: 16)wherein Y is C, T or, preferably, a mixture thereof, and R is A, G or,preferably, a mixture thereof.

For the diagnosis or prognosis of liver cancer, the step of amplifyingpreferably amplifies a target region within the region of the GST-Pigene and its regulatory flanking sequences defined by (and inclusive onCpG sites −43 to −14 and/or +9 to +53. However, within these targetregions it is believed that there are CpG sites which show variabilityin methylation status in liver cancer or are methylated in othertissues. Thus, for the target region defined by (and inclusive of) CpGsites −43 to −14, it is preferred that the primers used foramplification be designed so as to minimise (i.e. by use of redundantprimers or by avoidance of the sites) the influence of CpG sites −36,−32, −23, −20, −19, −14 and a polymorphic region covering site −33.

It will be appreciated by persons skilled in the art, that a site orsites of abnormal cytosine methylation within the above identifiedtarget regions of the GST-Pi gene and/or its regulatory flankingsequences, could be detected for the purposes of diagnosing orprognosing a disease or condition (particularly, prostate cancer and/orliver cancer) by methods which do not involve selective amplification.For instance, oligonucleotide/polynucleotide probes could be designedfor use in hybridisation studies (e.g. Southern blotting) withbisulphite-treated DNA which, under appropriate conditions ofstringency, selectively hybridise only to DNA which includes a site orsites of abnormal methylation of cytosine(s). Alternatively, anappropriately selected informative restriction enzyme(s) could be usedto produce restriction fragment patterns that distinguish between DNAwhich does and does not include a site or sites of abnormal methylationof cytosine(s).

Thus, in a second aspect, the present invention provides a diagnostic orprognostic assay for a disease or condition in a subject said disease orcondition characterised by abnormal methylation of cytosine at a site orsites within the glutathione-S-transferase (GST) Pi gene and/or itsregulatory flanking sequences, wherein said assay comprises the stepsof;

-   (i) isolating DNA from said subject, and-   (ii) determining the presence of abnormal methylation of cytosine at    a site or sites within the region of the GST-Pi gene and/or its    regulatory flanking sequences defined by (and inclusive of) CpG    sites −43 to +55.

The step of isolating DNA may be conducted as described above inrelation to the assay of the first aspect.

Preferably, the region of the GST-Pi gene and its regulatory flankingsequences within which the presence of methylated cytosine(s) at a siteor sites is determined is selected from the regions defined by (andinclusive of) CpG sites −43 to +53, −43 to +10, −43 to −14, +9 to +53and +1 to +53. However, within these regions, it is preferred thatcertain sites (namely, CpG sites, −36, −33, −32, −23, −20, −19, and −14)be avoided as the site or sites at which, for the purpose of the assay,the presence of abnormal methylation of cytosine is determined.

Where the determination step is to involve selective hybridisation ofoligonucleotide/polynucleotide/peptide-nucleic acid (PNA) probes, priorto the determination step, the isolated DNA is preferably treated (e.g.with bisulphite) such that unmethylated cytosines are converted touracil or another nucleotide capable of forming a base pair with adeninewhile methylated cytosines are unchanged or are converted to anucleotide capable of forcing a base pair with guanine. This treatmentpermits the design of probes which allow for selective hybridisation toa target region including a site or sites of abnormal methylation ofcytosine.

In a third aspect, the present invention provides a primer or probe(sequence shown in the 5′ to 3′ direction) comprising a nucleotidesequence selected from the group consisting of:CGCGAGGTTTTCGTTGGAGTTTCGTCGTC (SEQ ID NO: 1) CGTTATTAGTGAGTACGCGCGGTTC(SEQ ID NO: 2) YGGTTTTAGGGAATTTTTTTTCGC (SEQ ID NO: 3)YGGYGYGTTAGTTYGTTGYGTATATTTC (SEQ ID NO: 4)GGGAATTTTTTTTCGCGATGTTTYGGCGC (SEQ ID NO: 5) TTTTTAGGGGGTTYGGAGCGTTTC(SEQ ID NO: 6) GGTAGGTTGYGTTTATCGC (SEQ ID NO: 7)AAAAATTCRAATCTCTCCGAATAAACG (SEQ ID NO: 8) AAAAACCRAAATAAAAACCACACGACG(SEQ ID NO: 9) TCCCATCCCTCCCCGAAACGCTCCG (SEQ ID NO: 10)GAAACGCTCCGAACCCCCTAAAAACCGCTAACG (SEQ ID NO: 11)CRCCCTAAAATCCCCRAAATCRCCGCG (SEQ ID NO: 12)ACCCCRACRACCRCTACACCCCRAACGTCG (SEQ ID NO: 13)CTCTTCTAAAAAATCCCRCRAACTCCCGCCG (SEQ ID NO: 14)AAAACRCCCTAAAATCCCCGAAATCGCCG (SEQ ID NO: 15)AACTCCCRCCGACCCCAACCCCGACGACCG (SEQ ID NO: 16)

wherein Y is C, T or, preferably, a mixture thereof, and R is A, G or,preferably, a mixture thereof.

The terms “comprise”, “comprises” and “comprising” as used throughoutthe specification are intended to refer to the inclusion of a statedcomponent, feature or step or group of components, features or stepswith or without the inclusion of a further component, feature or step orgroup of components, features or steps.

The invention will now be further described with reference to theaccompanying figures and following, non-limiting examples.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

FIG. 1 shows the organization and nucleotide sequence of human GST-Pigene (SEQ ID NO: 60). CpG sites are numbered relative to thetranscription start site. Nucleotide Sequence numbering is according tothe GST-Pi gene sequence of GenBank Accession No. M24485.

FIG. 2 shows the region of the GST-Pi gene exhibiting differentialmethylation in prostate cancer. The figure further shows the sequenceand derivation of primers for the upstream region (from CpG site −43 to+10) and the common polymorphism encompassing CpG site −33 (shown abovethe sequence (p)). Underneath the GST-Pi sequence is shown the sequenceof the derived strand after conversion of cytosines to uracil. Thederived strand is shown either assuming all CpGs are methylated (B-M) orun-methylated (B-U). Below this is shown specific pruners designed toselectively amplify the methylated sequence.

FIG. 3 shows the methylation status of each CpG site in isolated DNAs;

A—for the core promoter region through to the 3′ end of the GST-Pi genefor the LNCaP (LN) cell line, DU145 (DU) cell line, PC3 cell line, PC3-Mcell line and PC3-MM cell line, for DNA isolated from normal tissuesamples from prostate cancer patients (2AN, BN and CN), for prostatetumour tissue (BC, CC, DC, XC, WC and 2AC) and for normal prostatetissue (Pr) from a person without prostate cancer:

B—for the core promoter region and upstream sequences of the GST-Pi genefrom normal prostate tissue (from a person without prostate cancer),from three prostate cancer samples (BC, CC and DC) and for a number ofother normal tissues. Patients B and D were polymorphic at CpG site −33and the level of methylation indicated in the brackets reflectsmethylation of the allele which contains the CpG. For CpG sites −28 to+10, the level of methylation was determined by direct sequence analysisof the population of PCR molecules (17). For the upstream CpG sites, −56to −30, PCR products were cloned and a number of individual clonessequenced (number indicated in brackets below the sample name). Fornormal tissues the level of methylation at each site was determined asthe fraction of all clones containing a C at that position. For thecancer samples BC, CC and DC, the level of methylation shown is thatamong the clones which showed DNA methylation in the region from CpGsite −43 to −30 (about half of the clones in each case).

In both A and B, a blank box indicates that the site was not assayed,and a “B” indicates that the status of the site could not be determined(e.g. because of a sequence blockage or it was beyond the range of thesequencing run). The level of methylation detected at each site isshown, none (−), up to 25% (+), 26-50% (++), 51-75% (+++) and 76-100%(++++). The Gleason Grade of tumlour samples is also shown.

FIG. 4 provides the results of amplification of bisulphite treated DNAsfrom a variety of tissues;

A—panel A (region covering the transcription start site) used CGPS-1 and3 as outer primers and CGPS-2 and 4 as inner primers, Panel B used theouter primer pair CGPS-5 and 8 which encompass the region from CpG site−39 to −16 for first round amplification, followed by a second round ofamplification with the CGPS-6 and 7 primers, amplifying a 140 bpfragment covering CpG sites −36 to −23. The lanes are 1. Brain. 2. Lung,3. Skeletal muscle, 4. Spleen, 5. Pancreas. 6. “Normal” Prostate Aged 85y.o., 7. “Normal” Prostate Aged 62 y.o. 8. Heart. 9. Bone Marrow, 10.Blood-1, 11. Blood-2, 12. Blood-3, 13. Liver-1, 14. Liver-2;

B—used the same primer pairs as that of the amplification shown in FIG.4A Panel B, with DNA from 10 prostate cancer tissue samples (c) andmatched normal (n) tissue samples from the same prostates (a positivecontrol (+) LNCaP DNA and a negative control (−) is also shown).Underneath, is the Gleason grade and the level of methylation of samplesseen with non-selective primers.

C—used the same primer pairs as that of the amplification shown in FIG.4A Panel B. at with DNA from a range of healthy tissues, blood fromprostate cancer patients and various cell lines. The lanes are: Panel A1-10 blood samples from prostate cancer patients during radicalprostacectomy; Panel B 1. normal prostate-1, 2. normal prostate-2, 3.normal prostate-3, 4. normal prostate-4, 5. normal prostate-5, 6. HPVtransformed prostate cell line, 7. blood from prostate patient PA(PSA=1000), 8. blood from prostate patient PB (PSA=56). 9. blood fromprostate patient PC (PSA=18); and Panel C 1. LNCaP cell line, 2. Du145cell line, 3. PC-3 cell line, 4. PC-3M cell line, 5. PC-3MM cell line,6. Hela cell line, 7. leukemic DNA, 8. HepG2 cell line, 9. human liverDNA, 10. white blood cells, 11. MRC-5 cell line.

FIG. 5 provides the results of amplification of bisulphite treated DNAsfrom seminal fluid of prostate cancer patients (c) and from men with nodiagnosed prostate cancer (n), using the outer primer pair CGPS-5 and 8and CGPS-6 and 7 as the inner primer pair. The lanes are L. LNCaP cellline (positive control), D. DU145 cell line, P. PC-3 cell line (negativecontrols), and M. molecular weight markers.

FIG. 6 shows the results of amplification of bisulphite treated DNAs,wherein the DNA has been isolated from prostate tissue slides that hadbeen identified as either cancerous or diseased with benign hyperplasia(BPH). Selective PCR amplification was conducted using the outer primerpair CGPS-5 and 8 and the inner primer pair CGPS-11 and 12.

FIG. 7 shows the results of amplification of bisulphite treated DNAs,wherein the DNA has been isolated from prostate cancer cells enrichedfrom blood samples using magnetic beads coated with an anti-epithelialantibody. Different numbers of LNCaP prostate cancer cells were added tothe blood samples (7A) or blood with added LNCAP cells stored fordifferent times at 4° C. or room temperature prior to DNA isolation.

FIG. 8 provides the results of amplification of bisulphite treated DNAs,wherein the DNA has been isolated from blood samples from normalsubjects with no known prostate complaint, from patients with benignhyperplasia (BPH) of the prostate and from patients with histologicallyconfirmed prostate cancer.

FIG. 9 shows the results of amplification of bisulphite treated DNAsisolated from 20 liver cancer tissue samples. Selective PCRamplification was conducted using the outer primer pair CGPS-5 and 8 andthe inner primer pair CGPS-11 and 12.

FIG. 10 shows the results of tests conducted to confirm that anyamplified DNA products has occurred from amplification of bisulphitetreated DNA wherein all unmethylated cytosine has been converted touracil. The tests are conducted using oligonucleotides probes designedto hybridise to converted or non-converted target regions.

GENERAL METHODS AND STRATEGIES

(1) Treatment of DNA with bisulphite

DNA for assaying was isolated from suitable sources by standardprotocols and treated with bisulphite by well known methods (12, 13,16).

(2) Characterisation of Methylation of Individual Sites in DNA

In order to determine the methylation status of individual cytosinenucleotides in target and non-target DNAs and to identify differencesbetween them, bisulphite-modified DNA was amplified by PCR using primersdesigned to minimise the possibility that the methylation status of aparticular CpG site will influence primer annealing and subsequentamplification (12, 13, 16).

(3) Design of Selective Primers

Based oil the sequencing information, primers for use in the assay weredesigned to maximise the possibility that the methylation status of aparticular CpG site would influence primer annealing and subsequentamplification. Specifically, the design principles followed (describedfor the “forward” PCR primer where the primer contains the same C to T(or U) conversions as would occur in the bisulphite-treated DNA), arelisted below at (a) to (d):

(a) That primers should cover sequence regions which contain a number ofC's. Conversion of unmethylated C's to Us provides for discriminationbetween molecules which have undergone efficient bisulphite conversionand molecules in which C's have not reacted (e.g. because not completelydissolved or containing regions of secondary structure).

(b) That at least one, but preferably at least two to four, of the C'sin the regions should be C's (generally at CpG sites) known to bemethylated in a high proportion of the DNA to be detected (i.e. targetDNA). Thus, these C's will remain C's in the target DNA while beingconverted to U's in the non-target DNA. A primer which is designed to bethe exactly equivalent of the bisulphite-converted methylated DNA willcontain a mismatch at each of the positions of an unmethylated C whichhas been converted to a U in an unmethylated DNA. The more mismatchesthat are present, the greater the differential hybridisation stabilityof the primers will be and hence the greater the selective difference inPCR.

(c) That the 3′ terminal base of the primer should preferably be a Ccorresponding to a C known to be methylated in the target DNA (normallypart of a CpG dinucleotide). Correct pairing with the terminal base ofthe primer will provide for highly selective priming of target sequencescompared with unmethylated background sequences which will form a C:Amismatch.

(d) That at positions where it is known that methylation occurs in onlya fraction of molecules in the methylated target DNA or where it isknown to vary between target DNAs (e.g. in different tumour samples),redundancy can be incorporated into the primers to allow foramplification of either C or T from the target DNA. This same approachcan be used if polymorphisms are known to exist in the primer region.

For the “reverse” primer, which anneals to the converted strand, A'sreplace G's at positions opposite converted C's

(4) Verification of Selective Target Sequence Amplification

The amplified PCR band can be analysed to verify that it has beenderived from DNA which has been fully bisulphite-converted (i.e. C's notmethylated in the original DNA have been converted to U's and amplifiedas T's) and to further verify that the amplified DNA has been derivedfrom the specific target DNA sequence and has the expected methylationprofile (i.e. 5meC's not converted to T's). Methods for conducting theseverifications include:

(a) Using Restriction Enzyme Digestion.

In order to verify complete conversion, particular restriction enzymescan be used to cut the DNA. The sequence recognition sites should havethe property that they contain no C's and are present in the sequence ofthe amplified strand after but not before bisulphite treatment. Thus,the conversion of one or preferably two or more C's to U's and theiramplification as T's in the PCR product should produce a new restrictionsite. Useful enzymes are shown in italics in Table 1 below.

In order to verify that the target DNA sequence amplified wasspecifically methylated, use can be made of restriction enzyme siteswhose only C nucleotides are found as CpG dinucleotides and which, ifthe sequence was methylated, would remain as CpG's in the PCR products.Examples of such enzymes are shown in bold in Table 1 below. BsnBI,which cuts the non-symmetrical sequence GAGACG can also be used.

In some instances, enzymes which contain a C as an outer base in theirrecognition sequence can be used for verification of methylation: e.g.EcoRI (GAATTC) for a GAATTCG sequence or Sau3AI (GATC) for a GATCGsequence (bold and underlined in Table 1). If a site such as one of theabove is present in the predicted methylated, fully bisulphite-convertedDNA then the enzyme will cut the DNA only if the original CpGdinucleotide was methylated, confirming the amplification of amethylated region of DNA. Some of the enzymes (bold and underlined inTable 1) have the potential to be used both for monitoring efficientconversion and CpG methylation.

(b) Differential Hybridisation to Specific Oligonucleotides.

Differential hybridisation to specific oligonucleotides can be used todiscriminate that the amplified DNA is fully reacted with bisulphite andof the expected methylation profile. To demonstrate complete conversion,a pair of oligonucleotides corresponding to the same region within theamplified sequence is prepared. One oligonucleotide contains T's at allC's which should be converted by bisulphite, while the other containsC's in these positions. The oligonucleotides should contain at least twoor three of such discriminatory C's and conditions be determined whichprovide for selective hybridisation of each to its target sequence.Similar oligonucleotides with C or T at CpG sites and T's replacing allnon-CpG C's are used to determine whether the specific CpG sites aremethylated. Additional control oligonucleotides that contain nodiscriminatory C's, that is, either no C's or a minimal number where C'sare substituted with Y's (mixture of C and T), are used to monitor theamount of PCR product in the sample. The oligonucleotides can be usedfor direct hybridisation detection of amplified sequences or used toselect out target molecules from the PCR-amplified DNA population forother detection methods. An array of such oligonucleotides oil a DNAsequencing chip can be used to establish the sequence of the amplifiedDNA throughout the sequence region.

(c) Single Nucleotide Primer Extension (SNuPE).

The technique of single nucleotide primer extension can be applied tothe PCR products to determine whether specific sites within theamplified sequence contain C or T bases. In this method, a primerabutting the position of interest is annealed to the PCR product andprimer extension reactions performed using either just dCTP or justdTTP. The products can be separated by gel electrophoresis andquantitated to determine the proportion of each nucleotide in thepopulation at that position. Primers should be designed to quantitateconversion of C's in CpG sites and control C's which should not bemethylated. More than one primer can be included in a single reactionand/or run in the same gel track as long as their sizes can be clearlydistinguished.

(d) Fluorescent Real-time Monitoring of PCR.

Oligonucleotides internal to the amplified region can be used to monitorand quantify the amplification reaction at the same time asdemonstrating amplification of the correct sequence. In the Fluorogenic5′ Nuclease PCR assay (19) the amplification reaction is monitored usinga primer which binds internally within the amplified sequence and whichcontains both a fluorogenic reporter and a quencher. When this probe isbound to its target DNA it can be cleaved by the 5′ nuclease activity ofthe Taq polymerase, separating the reporter and the quencher. Byutilising in the assay all oligonucleotide which is selective for thefully bisulphite-converted sequence (and/or its methylation state) boththe level of amplification and its specificity can be monitored in asingle reaction. Other related systems that similarly detect PCRproducts by hybridisation can also be used.

EXAMPLE 1 Methylation Sequence Profile of Target and Non-target GST-PiDNA

Materials and Methods

FIG. 1 shows the organisation of the GST-Pi gene and the regions forwhich genomic sequencing was used to determine the methylation status ofDNA isolated from prostate cancer tissue or cell lines and from normalprostate or other tissues. The nucleotide sequence numbering in FIG. 1is according to the GST-Pi sequence, GenBank Accession No. M24485. Alsoshown, within the boxes is the sequence of each amplified region, withall the CpG sites indicated and numbered relative to the position of thetranscription start site. Sequence analysis demonstrated that there wasan additional CpG dinucleotide (+9) not predicted from the publishedsequence. Also identified in the regions sequenced was a polymorphismwhich is present in a significant fraction of the samples studied. Thepolymorphic allele does not contain CpG site −33. Both the additionalCpG dinucleotide and the polyymorphism are shown in FIG. 2. Thenucleotide coordinates in FIG. 2 are shown relative to the transcriptionstart site; the first base shown, −434, corresponds to base 781 of theGenBank sequence, while the last +90, corresponds to base 1313 of theGenbank sequence.

Table 2 lists the sequences and positions of the non-selective primersused for amplification (Table 2-1) and direct sequencing (Table 2-2) ofbisulphite-treated DNA.

DNA isolated from normal prostate tissue, prostate cancer tissue,prostate cancer-derived cell lines and other tissues was bisulphitetreated and PCR reactions done by standard procedures (13). PCR productswere either digested with informative restriction enzymes, sequenceddirectly (17), or individual molecules cloned and sequenced by standardprocedures.

Results

In FIG. 3A, the methylation status of sites in DNA from prostate cancercell lines, prostate cancer tissue samples and matched normal prostatetissue are shown for the core promoter regions through to the 3′ end ofthe gene (covering CpG sites −28 to 103). It can be seen that in normalprostate tissue, the core promoter region is unmethylated at all sitesand that this lack of methylation extends through the region flankingthe promoter to CpG site +33. Results of restriction enzyme digests ofbisulphite-treated, PCR-amplified DNA indicate that this lack ofmethylation includes CpG sites +52 and +53. However, in the regionsfurther downstream which were analysed, CpG sites +68 to +74 and +96 to+103, DNA from normal prostate tissue was heavily methylated. Analysisof the prostate cancer cell line LNCaP and prostate cancer tissuesamples demonstrates extensive methylation of the core promoter region;variations in the overall level of methylation probably reflect thepresence of different levels of normal cells within the tumour samples.DNA from one cancer sample (2AC) was found to be completely unmethylatedand in contrast to the other tumour samples this tumour was found byimmunohistochemistry to still be expressing GST-Pi. Sequencing of theregion flanking the core promoter in the LNCaP cell line and tumourDNAs, BC and CC, showed that methylation extended through to CpG site+33 and further restriction enzyme analysis showed that methylationincluded CpG sites +52 and +53. For one tumour sample, DC, methylationdid not extend beyond the core promoter region and CpG sites +13 to +33,as well as CpG sites +52 and +53 were found to be unmethylated. It isnotable that this tumour was of Gleason Grade 2+2, the lowest gradetumour among those analysed. For all tumour DNA samples, as for thenormal DNA, the downstream regions of the gene, sites 68 to 74 and 96 to103 , were heavily methylated. Within the promoter regions which weremethylated in the cancer, but not normal, tissue specific individualsites were evident which were either unmethylated or methylated to amuch lower degree than surrounding methylated sites. These include sites−22 and −23 (XC), −20 (PC3 lines, XC and WC), −14 (PC3, XC and WC), +24(PC3-M and MM2, CC), +25 (LNCaP, PC3-MM2. CC).

The results shown in FIG. 3B provides a comparison of the methylationstate of the core promoter region and sequences upstream of the corepromoter region in DNA isolated from normal prostate tissue and front anumber of other normal tissues. Sequences from the PCR fragment upstreamof the core promoter were determined by cloning and sequencing as theregion is refractory to direct sequencing. For the cancer samples, thelevel of methylation shown is as a proportion of those clones which weremethylated (about 50% of the total clones in both cases). In normalprostate tissue as well as in all other normal tissues there isextensive methylation of CpG sites upstream of the AT-rich repeat.Downstream of the repeat (from CpG site −43) minimal methylation wasseen in all normal tissues except normal liver tissue. where there wassignificant methylation of CpG sites −7 through to +7. Sequencesupstream of the core promoter were found to be heavily methylated in theprostate cancer DNAs, though again specific sites were undermethylated;site −32 in cancers B and D and site −36 in cancer B.

The results therefore allow for the identification of a region of theGST-Pi gene and its regulatory flanking sequences, stretching from 3′ ofthe polymorphic repeat region, (CpG site −43) to sites +52 and +53,which is not methylated in normal prostate tissue but is normally highlymethylated in prostate cancer. In one cancer sample (D, the cancer oflowest Gleason Grade) the region from CpG sites +13 to +53 was notmethylated. The more restricted region extending from CpG site −43 to+10 was methylated in all of the prostate cancer DNAs which showedpromoter methylation. Methylation of part of the promoter region (CpGsites −7 to +7) was also seen in one normal tissue (liver) examined.Analysis of further samples of normal liver DNA has shown that the levelof methylation is variable and can include CpG sites from -13 to +8.

Discussion

The above results are critical in identifying regions within the GST-Pigene and/or its regulatory flanking sequences which can be used for thedevelopment of assays for the selective detection of prostate cancercells. Thus, the region from CpG sites −43 to +53 lying within theboundary of regions methylated in normal prostate tissue can be used forthe design of primers to detect cancer-specific methylation in prostatetissue samples. The region from CpG site −43 to +10 is preferred for thedetection of a higher proportion of cancers. The region from CpG sites+13 to +53 may be used to detect cancer but also may be used todistinguish early (unmethylated) cancer from later (methylated cancer).For assays using other samples, such as blood, it is preferred torestrict the region chosen to exclude CpG sites −7 to +7 or, morepreferably sites −13 to +8. For example, liver cells maybe present inthe blood taken from a subject suffering liver disease, in which case, afalse positive result could be obtained if the region chosen fordetection of cancer-specific methylation includes CpG sites −13 to +8.

EXAMPLE 2 Design and Use of Selective Primers for Detection ofMethylated GST-Pi DNA

Materials and Methods

Sequence primers for the detection of methylated GST-Pi sequences fromthree regions, namely a region upstream of the core promoter (primersCGPS-5 to 9 and CGPS-11 to 13), a region partially encompassing the corepromoter (primers CGPS-1 to 4), and a region further downstream from thecore promoter (primers CGPS-21 to 24) are shown in Table 3 below.

The sequence and derivation of primers for the upstream region are shownin FIG. 2 (from CpG site −43 to CpG site +10), which also shows thecommon polymorphism encompassing CpG site −33 (see above the sequence(p)). Underneath is shown the sequence of the derived strand afterconversion of cytosines to uracil. The derived strand is shown eitherassuming all CpGs are methylated (B-M) or that none are (B-U). Belowthis is shown specific primers designed to selectively amplify themethylated sequence. It can be seen that all primers are designed tomatch perfectly to the treated, methylated template, but containmismatches to the template derived from unmethylated DNA or the originaluntreated DNA. Primers CGPS-5, 8, 11, 12 and 13 are designed to avoidthe polymorphic region and CpG sites which show a lower frequency ofmethylation in prostate cancer DNAs. The underlined T's in the forwardprimers (and A's in the reverse primers) derive from bisulphiteconversion of C's and provide discrimination against amplification ofDNA which has not been efficiently converted by the bisulphitetreatment. The bold C's in the forward primers (and G's in the reverseprimers) are parts of CpG sites and will form base pairs with DNAderived from methylated sequences but form mismatches to DNA derivedfrom unmethylated sequences. Redundancy is included in some positions, Y(=mix of C and T) in forward primers and R (=mix of A and G) in reverseprimers to allow pairing independent of methylation status. This canallow for certain sites where the frequency of methylation within orbetween tumour samples is variable (eg. site −14). Forward and reverseprimers for specific selective amplification of methylated GST-Pisequences are shown in Table 3 below.

Amplifications conducted for this example, utilised bisulphite treatedDNAs from a variety of tissues and used two sets of PCR primers.Specifically, for the amplification reactions shown in FIG. 4A Panel A(region covering the transcription start site), CGPS-1 and 3 were usedas outer primers and CGPS-2 and 4 as inner primers. For theamplification reactions shown in FIG. 4A Panel B and FIG. 4B and 4C, theouter primer pair, CGPS-5 and CGPS-8 which encompass the region from CpGsite −39 to −16, were used for first round amplification, followed bysecond round amplification with the CGPS-6 and CGPS-7 primers, resultingin the amplification of a 140 bp fragment covering CpG sites −36 to −23.For the amplification reactions shown in FIGS. 5 to 8, the primer setused for the upstream region was the outer primer pair, CGPS-5 andCGPS-8, for first round amplification and the inner primer pair, CGPS-11and CGPS-12, for second round amplification, resulting in theamplification of a 167 bp fragment covering CpG sites −38 to −23.

For all sets of primers, PCR amplifications were performed in a bufferconsisting of 67 μm Tris/HCl, 16.6 mM ammonium sulphate, 1.7 mg/ml BSAand 1.5 mM MgCl₂, prepared in TE buffer (10 mM Tris/HCl pH 8.8, 0.1 mMEDTA). Reaction mixes (50 μl) contained 200 μM of each of the fourdNTPs, 6 ng/ml of each primer and 2 units of AmpliTaq DNA polymerase(Perkin Elmer). For the primers CGPS-5 and 8 (first roundamplification), PCR cycle conditions were 5 cycles of 60° C. 1 min., 72°C. 2 mil. and 95° C. 1 min., followed by 30 cycles of 65° C. 1 min., 72°C. 1.5 min. and 95° C. 1 min. Amplification conditions for the primersCGPS-6 and 7 (second round amplification) were 5 cycles of 65° C. 1min., 72° C. 2 min. and 95° C. 1 min., followed by 30 cycles of 65° C. 1min., 72° C. 1.5 min. and 95° C. 1 min. For the primers CGPS-11 and 12,the amplification conditions were the same as for the CGPS-6 and 7primers except that the annealing temperature was raised from 65° C. to70° C. 2 μl of the first round amplification reactions were used in 50μl of second round amplification reactions. Other buffers or PCRamplification conditions may also be used to achieve similar efficiencyand specificity.

Results and Discussion

For the primers covering the core promoter region (see FIG. 4A Panel A),amplified DNA (see arrowed band) was obtained from the positive controlDNA (cancer B) but also from DNA from prostate tissue samples from twosubjects who had not been diagnosed with prostate cancer. Bands ofamplified DNA were also seen from DNA isolated from a bone marrow andblood sample as well as from DNA isolated from liver tissue samples fromsubjects with no known prostate cancer.

For the upstream amplification (see FIG. 4A Panel B), no amplified DNAwas obtained from amplification reactions conducted on DNA isolated froma range of healthy tissue samples nor from DNA isolated from bloodsamples of subjects with no known prostate cancer; a band of amplifiedDNA was produced from the positive control DNA (cancer B). However,while amplification reactions conducted on DNA isolated from one normalprostate tissue sample did not result in amplified DNA, amplified DNAdid result from the same amplification reactions conducted oil DNAisolated from a prostate tissue sample of an 82 year old subject with noknown prostate cancer. It is possible that this subject had undiagnosedprostate cancer. DNA isolated from five other samples of normal prostatetissue from subjects with no known prostate cancer did not give rise toall amplified DNA product (see FIG. 4C Panel B).

In FIG. 4B, the results of PCR amplification reactions are shown fortissue samples from patients with prostate cancer: for each sample, DNAwas isolated from a region identified as containing cancer and fromanother region identified as grossly normal. In all cases, a clear bandof amplified DNA was produced from amplification reactions conducted onprostate cancer DNA. Two of these, were cases where the proportion ofmethylated DNA was insufficient to be detected using primers designed toprime equivalently on methylated and unmethylated DNA. For DNA isolatedfrom grossly normal tissue, the band of amplified DNA was either absentor present in a substantially lower amount. The presence of a band insome “normal” samples could derive from a low level of cancer cells inthe sample.

Amplification of DNA from samples of blood obtained from the abdominalcavity during surgery showed that it was possible to detect methylatedGST-Pi sequences in a number of them. Samples of peripheral bloodisolated from three patients with known metastatic disease (see FIG. 4CPanel B) demonstrated the presence of amplifiable, methylated GST-Pisequences.

Amplified DNA products were also produced from amplification of DNAisolated from the LNCaP and DU145 prostate cancer cell lines, but notfrom the PC-3 series of cell lines. This latter result could be due to alow level of methylation in the upstream promoter region in PC-3 cells,but a major contributing factor is likely to be a lack of printing bythe CGPS-6 primer as PC-3 only contains the variant allele of the GST-Pigene. Methylated GST-Pi sequences were also detected in DNA isolatedfrom some tumour-derived cell lines of non-prostatic origin: HeLa, acervical carcinoma, and HepG2, a liver carcinoma (see FIG. 4C Panel B).

DNA was isolated from the seminal fluid (see FIG. 5) of 3 prostatecancer patients (C) and from 5 subjects with no known prostate cancer(N), treated with bisulphite and amplified using primers CGPS-5 and 8followed by CGPS-6 and 7. Amplified DNA products were obtained from allthree cancer DNAs. One of the five samples from subjects withoutdiagnosed prostate cancer also resulted in an amplified DNA product, butit is not clear if this represents a false positive or a case ofundiagnosed prostate cancer in the particular subject.

The use of the primer CGPS-11 avoids annealing across the polymorphicsequence at CpG site −33, and the combination of CGPS-5 and 8 as outerprimers followed by CGPS-11 and 12 as inner primers was found to giveefficient amplification of prostate cancer DNA. In a first experiment(see FIG. 6), DNA was extracted from regions of fixed tissue slides thathad been identified as either being cancerous or being diseased withbenign hyperplasia (BPH). DNA was isolated by incubating scrapedmaterial in 400 μl of 7M guanidinium hydrochloride, 5 mM EDTA, 100 mMTris/HCl pH 6.4, 1% Triton-X100, 50 mg/ml proteinase K and 100 mg/mlyeast tRNA. After homogenisation, samples were incubated for 48 hours at55° C. then subjected to five freeze/thaw cycles of dry ice for 5min./95° C. for 5 min. After vortexing and centrifugation for 2 min. ina microfuge, the supernatants were then diluted three fold, extractedwith phenol/chloroform and ethanol precipitated. DNA isolated fromsamples from 6 cancer patients and 4 with BPH were amplified with eithernon-selective primers for the core promoter region (i.e. control PCRamplification with GST-9 and 10 followed by GST-11 and 12) or CGselective primers (i.e. selective PCR amplification with CGPS-5 and 8followed by CGPS-11 and 12). Control PCR amplifications demonstrated thepresence of amplifiable DNA in all samples. Using the CG selectiveprimers, amplified DNA products were only obtained from the cancer DNAs.The PSA (prostate specific antigen) levels of these patients ranged from4 to 145 ng/ml. For the BPH patients, the PSA levels ranged from 2.3 to25 ng/ml.

In further experiments, prostate cancer cells were first enriched fromblood samples using antibodies coupled to magnetic beads followed by DNAisolation, bisulphite modification and PCR amplification. Cell isolationwas achieved using Dynabeads anti-Epithelial Cell (Dynal Prod. No.112.07) essentially as described by the manufacturer. The magnetic beadswere coated with the anti-epithelial antibody inAb Ber-EP4 (22).Alternatively, magnetic beads coupled to antibodies specific for theextracellular domain of the prostate specific membrane antigen (23)could have been used. Whole blood was diluted 1:1 with Dulbecco'sphosphate buffered saline (PBS) containing 10 mM EDTA and 40 μl ofpre-washed magnetic beads added. Cells were incubated at 4° C. on arotating platform for 30 min and then the beads were collected to theside of the tube using a magnetic cell separation device for 4 min. Thesupernatant was then carefully aspirated and the beads resuspended inthe washing solution (PBS containing 0.5% bovine serum albumin). Beadswere then again collected to the side of the tube using a magnet and thesupernatant carefully aspirated before conducting a further wash wasdone with the tube remaining in place in the magnetic separation deviceand the supernatant aspirated. The beads were then resuspended in DNAisolation buffer (100 mM Tris/HCl pH 8, 25 mM EDTA, 1% Sarkosyl, 200mg/ml proteinase K), incubated for at least 2 h at 37° and DNA recoveredby phenol/chloroform extraction and ethanol precipitation. The DNA wasthen finally subjected to bisulphite treatment and PCR amplification.

The sensitivity of this method was tested by seeding varying numbers ofcells of a prostate cancer cell line, LNCaP, into normal blood. As shownin FIG. 7A, the presence of 20 cells or more in 0.5 ml of blood could bereliably detected. The experiment shown in FIG. 7B showed that bloodsamples containing LNCaP cells could be stored at room temperature or at4° C. for up to 24 hours without loss of sensitivity.

Using magnetic bead capture followed by bisulphite treatment andselective PCR amplification, patient blood samples were also analysedand the results from a set of these are shown in FIG. 8. These includeblood samples from normal subjects with no known prostate complaint,from patients with benign hyperplasia (BPH) of the prostate and frompatients with histologically confirmed prostate cancer. The control PCRamplifications (upper panel) used primers which amplify both methylatedand unmethylated GST-Pi sequences. The amplifications using CG-selectiveprimers are shown in the lower panel. Positive control amplifications(LNCaP (L) and PC3 (P)) are shown in the cancer panels and negativecontrol amplifications are shown in the normal and cancer panels.

Table 4 below summarises the results of testing of DNA from patientblood samples using the magnetic bead/CG selective PCR amplificationprotocol. No amplified DNA products were obtained from DNA isolated fromnormal control subjects, and only DNA isolated from one of 18 patientsdiagnosed histologically to have BPH produced amplified DNA products(this patient had a blood PSA level of 17 ng/ml). Of patients withconfirmed prostate cancer, isolated DNA from 17 of 24 (70%) werePCR-positive (i.e. resulted in the production of amplified DNA),indicating the presence of prostate cancer cells in the blood. Forpatients clinically staged as A and B, (i.e. disease confined to theprostate), cancer cells were detected in the blood in 6 of of the 10cases. For 9 patients with locally invasive (Stage C) or metastatic(Stage D) disease, cancer cells were detected in the blood in everycase.

Since it was found that the HepG2 liver cancer cell line containedmethylated GST-Pi sequences, samples of DNA isolated from liver cancertissue was also examined. DNA isolated from 20 liver cancer samples werebisulphite treated and amplified using the CGPS-5 and 8 and CGPS-11 and12 primer pairs (see FIG. 9). 14 of the 20 samples were PCR-positive. Onthe other hand, no amplified DNA products were produced from DNAisolated from 2 patients with no liver cancer (see FIG. 4 and data notshown). DNA isolated from normal liver tissue was shown to be partiallymethylated in the region of the transcription start site (CpG sites −7to +7, see FIG. 3B). Analysis of further samples of normal liver DNA hasshown that the level of methylation is variable and can include CpGsites from −13 to +8. The primer pairs used here encompass CpG sites −39to −16, upstream of the region of methylation seen in normal liver DNA.

The above results show that different sets of primers designed tohybridise the core promoter of the GST-Pi gene or the region upstream ofthe core promoter, can reliably amplify bisulphite-treated DNA that hasbeen isolated from prostate cancer cells. However, primers designed tohybridise to the core promoter are less selective in that DNAs isolatedfrom a number of normal tissue samples result in amplified DNA products.Thus, primers designed to hybridise to regions found to be unmethylatedin DNA from normal tissues, that is, the upstream region encompassingCpG sites 45 to −8 and the region downstream of the promoterencompassing CpG sites +8 to +53, are preferred for the prognostic ordiagnostic assaying of prostate cancer. Additionally, primers designedto hybridise to this latter region may also be useful for discriminatingbetween early and late prostate cancer.

EXAMPLE 3 Confirmation of Correct Amplification

The specific oligonucleotides probes described below can be used toconfirm that any amplified DNA products resulting from the amplificationstep of the assay is due to DNA in which all unmethylated cytosines hadbeen converted to uracils. Those for the upstream PCR region can be usedwith amplified DNA products from all combinations of the CGPS-5, 6, 11,7 to 9, 12 and 13 forward and reverse primers. Those for the downstreamPCR region can be used with amplified DNA products of the CGPS-21 to 24primers. A biotinylated version of the conversion-specificolignucleotide can also be used for the selective and specific capturefrom solution of the amplified DNA products generated using these primerpairs, or the appropriately labelled oligonucleotide can be use forreal-time monitoring of specific PCR fragment amplification. AmplifiedDNA products from PCR amplification of bisulphite-treated DNA routinelyhave one strand containing a very high proportion of thymine nucleotidesand the other strand containing a very high proportion of adeninenucleotides. Because of this, it is possible to use oligo dT (or oligodA) as a generic conversion specific oligonucleotide, the annealingconditions being varied to optimise discrimination of converted andnon-converted DNA for each PCR fragment.

Upstream PCR Region:

Conversion Oligonucleotide: HybC5 5′-AAACCTAAAAAATAAACAAACAA (SEQ ID NO:17)

Non-conversion Oligonucleotide: HybU5 5′-GGGCCTAGGGAGTAAACAGACAG (SEQ IDNO: 18)

Conversion Neutral Oligonucleotide: (SEQ ID NO: 19) HybN5:5′-CCTTTCCCTCTTTCCCARRTCCCCADownstream PCR Region:

Conversion Oligonucleotide: (SEQ ID NO: 20) HyBC35′-TTTGGTATTTTTTTTCGGGTTTTAG

Non-conversion Oligonucleotide: (SEQ ID NO: 21) HybU35′-CTTGGCATCCTCCCCCGGGCTCCAG

Conversion Neutral Oligonucleotide: (SEQ ID NO: 22) HybN35′-GGYAGGGAAGGGAGGYAGGGGYTGGG

To demonstrate the selectivity of such hybridisations, a series of DNAswere spotted onto nylon membranes and hybridised with conversion andnon-conversion specific oligonucleotide probes for the upstream PCRregion as well as a control oligonucleotide. The DNAs included:

-   (i) individual cloned PCR products from amplification of the    upstream region that contained differing numbers of converted    cytosines in the region complementary to the probe (see FIG. 10,    where the number of converted cytosines, out of 10, is shown (Column    1 and top 2 spots of Column 2). n.b. the two clones containing 10/10    converted bases end adjacent to and do not contain the sequences    complementary to the control oligonucleotide); and-   (ii) PCR products from cancer patients and patients with benign    hyperplasia that had been amplified from bisulphite-treated DNA    using CG-selective primers (CGPS-5 and 8, followed by CGPS 11    and 12) (see FIG. 10, where these are labelled as Cancer Samples 1    to 4 (lower part of column 2) and BPH samples 1 to 4 (Column 3)).

Hybridisations with kinased oligonucleotide probes were performed inExpress-Hyb buffer (Clontech) at 45° C. for two hours followed by four20 min. washes in 2×SSC, 0.1% SDS at 45° C. before phosphorimageanalysis.

Hybridisations with the control oligonucleotide probes provides anestimate of the amount of DNA in the sample. As expected, none of thePCR amplifications of BPH samples produced significantly detectableproduct, while 3 of 4 cancer samples gave a strong signal and one a veryweak one, Hybridisations with the conversion-specific probe showed aclear signal for the plasmid DNAs that matched the probe perfectly andfor the 3 cancer samples for which there was stronger hybridisation withthe control oligonucleotide probe. The fourth cancer sample that gave avery weak signal with the control oligonucleotide was barely detectablewith the conversion-specific probe. This could have been due to the lowlevel of DNA or, possibly, the presence of partially-converted DNAmolecules. None of the plasmid clones that had mismatches to theconversion-specific probe gave a significant signal. The probe forunconverted DNA hybridised clearly with plasmid DNAs that had 0, 1 or 2bases converted, but not with samples that had 8 or 10 converted bases.The hybridisations also indicated that there was a low levelamplification of unconverted DNA in two BPH and one cancer sample (inthis latter case there was a strong signal from probe for fullyconverted DNA, indicating that the PCR product was predominantly derivedfrom properly converted DNA).

The results show that oligonucleotides of the type used here candiscriminate between molecules that have been efficiently converted bybisulphite and those that have not. They can be used in a number offormats for detection of PCR products or prior to PCR or other detectionmethods to select out efficiently converted molecules of the targetregion from the total DNA population. The same approach can be used withprimers that distinguish CpG methylated DNAs (or their derivativescontaining C's) from unmethylated DNAs (containing U's or theirderivatives containing T's).

REFERENCES

-   1. H. S. Shapiro, Content of 6-methylaminopurine and    5-methylcytosine in DNA. G. D. Fasman, Ed., Handbook of    Biochemistry, Selected Data for Molecular Biology: Nucleic Acids.    (CRC Press, Boca Raton Fla., 1975).-   2. R. L. Adams, Burdoni, R. H., Molecular Biology of DNA methylation    (Springer Verlag, New York, 1985).-   3. Y. Gruenbaum, T. Naveh-Many, H. Cedar, A. Razin, Nature 292,    860-862 (1981).-   4. S. J. Clark, J. Harrison, M. Frommer, Nat Genet 10, 20-27 (1995).-   5. R. Holliday, J. E. Pugh, Science 187, 226-232 (1975).-   6. A. D. Riggs, Cytogenet. Cell Genet. 14, 9-25 (1975).-   7. M. Graessmann, A. Graessmann, in DNA Methylation: Molecular    Biology and Biological Significance J. P. J. H. P. Saluz, Ed.    (Birkhauser Verlag, Basel, Switzerland, 1993) pp. 404-424.-   8. C. Stirzaker, et al., Cancer Res 57, 2229-2237 (1997).-   9. K. D. Tremblay, K. L. Duran, M. S. Bartolomei, Mol Cell Biol    Molecular and Cellular Biology 17, 4322-4329 (1997).-   10. R. Y.-H. Wang, Gehrke, C. W. and Ehrlich, M., Nucl. Acids Res.    8, 4777-4790 (1980).-   11. R. Shapiro, B. Braverman, J. B. Louis & R. E. Servis, J. Biol.    Chem. 248, 4060-4064 (1973).-   12. M. Frommer, McDonald, L. E., Millar, D. S., Collis, C. M., Watt,    F., Grigg, G. W., Molloy, P. L. & Paul, C. L., Proc. Natl. Acad.    Sci. USA. 89, 1827-1831 (1992).-   13. S. J. Clark, Harrison, J., Paul, C. L., & Frommer, M., Nucl.    Acids Res. 22, 2990-2997 (1994).-   14. J. G. Herman, J. R. Graff, S. Myohanen, B. D. Nelkin & S. B.    Baylin, Proc Natl Acad Sci USA 93, 9821-9826 (1996).-   15. W. H. Lee, et al., Proc Natl Acad Sci USA 91, 11733-11737    (1994).-   16. S. J. Clark, M. Frommer, in Laboratory Methods for the detection    of mutations and polymorphisms in DNA. G. Taylor, Ed. (CRC press,    NewYork, 1997) pp.151-162.-   17. C. L. Paul, S. J. Clark, BioTechniques 21, 126-133 (1996).-   18. W. H. Lee, W. B. Isaacs, G. S. Bova & W. G. Nelson, Cancer    Epidemiol Biomarkers Prev. 6 443-450 (1997).-   19. P. M. Holland, R. D. Abramson, R. Watson & D. H. Gelfland, Proc.    Natl. Acad. Sci. USA 88, 7276-7280 (1991).-   20. F. Barany, Proc. Natl. Acad. Sci. USA 88, 189-193 (1991).-   21. R. D. Abramson and T. W. Myers, Curr. Opinion Biotechnol.    4,41-47 (1993).-   22. U. Latza, G. Niedobitek, R. Schwarting, H. Nekarda and H. J.    Stein, Clinical Pathology 43, 213-219 (1990).

23. H. Liu, P. Moy, S. Kim, Y. Xia, A. Rajasekaran, V. Navarro, B.Knudsen and N. H. Bander, Cancer Res. 57, 3629-3634 (1997). TABLE 1

TABLE 2.1 Primers for PCR Amplification of the Bisulphite-ModifiedGST-Pi Gene Target Primer Primer Primer size Anneal Genomic PCR # TargetName Type 5′        3′ (bp) ° C. Position −1 Upstream GST-1 OuterTTATGTAATAAATTTGTATATTTTGTATATG 646 50/50 381-411 Top Strand (SEQ ID NO:23) DNA GST-25 Inner TGTAGATTATTTAAGGTTAGGAGTT 499 50/50 495-519 (SEQ IDNO: 24) GST-3 Inner AAACCTAAAAAATAAACAAACAACAAA 499 50/50 967-993 (SEQID NO: 25) GST-4 Outer AAAAAACCTTTCCCTCTTTCCCAAATCCC 646 50/50  999-1027(SEQ ID NO: 26) 1 Exon 1 GST-9 Outer TTTGTTGTTTGTTTATTTTTTAGGTTT 34645/50 967-993 Top Strand (SEQ ID NO: 27) DNA GST-11 InnerGGGATTTGGGAAAGAGGGAAAGCTTT 307 45/50  999-1025 (SEQ ID NO: 28) GST-12Inner ACTAAAAACTCTAAACCCCATCCC 307 45/50 1280-1303 (SEQ ID NO: 29)GST-10 Outer AACCTAATACTACCTTAACCCCAT 346 45/50 1304-1329 (SEQ ID NO:30) 2 Exon 1 GST-B1 Outer AATCCTCTTCCTACTATCTATTTACTCCTAAA 387 50/55958-990 Bottom (SEQ ID NO: 31) Strand GST-B2 InnerAAAACGTAAAAAAAAAAAAAAAACTTCCC 314 50/55 999-1027 DNA (SEQ ID NO: 32)GST-B3 Inner TTGGTTTTATGTTGGGAGTTTTGAGTTTT 314 50/55 1285-1313 (SEQ IDNO: 33) GST-B4 Outer TTTTGTGGGGAGTTGGGGTTTGATGTTGT 387 50/55 1317-1345(SEQ ID NO: 34) 3 Exon 2/ GST-13 Outer GGTTTAGAGTTTTTAGTATGGGGTTAATT 69145/50 1287-1315 Exon 3 (SEQ ID NO: 35) Top Strand GST-14 InnerTAGTATTAGGTTAGGGTTTT 603 45/50 1315-1337 DNA (SEQ ID NO: 36) GST-15Inner AAGTCTAAGGCTAATCTACCAACAAGATA 603 45/50 1920-1892 (SEQ ID NO: 37)GST-16 Outer GAAAAAACTTTAAATAAACCCTCGTAGCA 691 45/50 1978-1950 (SEQ IDNO: 38) 4 Exon 5 GST-30 Outer GTTTTGTGGTTAGGTTGTTTTTTTAGGTGTTAG 34055/60 2346-2376 Top Strand (SEQ ID NO: 39) DNA GST-31 InnerGTTTTGAGTATTTGTTGTGTGGTAGTTTTT 265 40/45 2381-2416 (SEQ ID NO: 40)GST-32 Inner TTAATATAAATAAAAAAAATATATTTACAA 265 40/45 2617-2646 (SEQ IDNO: 41) GST-33 Outer GAACCCCCAATACCCAACCGTAATACAAATACTC 340 55/602653-2686 (SEQ ID NO: 42) 5 Exon 7 GST-28 OuterGGTTTTAGTTTTTGGTTGTTTGGATG 347 50/55 3845-3869 Top Strand (SEQ ID NO:43) DNA GST-27 Inner TTTTTTTGTTTTTAGTATATGTGGGG 287 50/55 3874-3899 (SEQID NO: 44) GST-28 Inner ATACTAAAAAAACTATTTTCTAATCCTCTA 287 50/554161-4132 (SEQ ID NO: 45) GST-29 Outer CCAAACTAAAAAGTCCAAAAAACCACTAA 34750/55 4192-4164 (SEQ ID NO: 46)

Bases arising due to C to U conversion by bisulphite treatment are shownin bold TABLE 2.2 Primers for Direct Sequencing of Amplified GST-Pi GenePGR Fragments Primer Primer Primer Target Anneal Genomic PCR # TargetName Type 5′        3′ size (bp) ° C. Position 1 Exon 1 GST-11 M13TGTAAAACGACGGCCAGTGGGATTTGGGAAAGAGGGAA 307 45/50 1003-1026 Top Strand(SEQ ID NO: 47) DNA GST-12 Biotin BioACTAAAAACTCTAAACGCCATCCC 307 45/501288-1313 2 Exon 1 GST-B2 M13 TGTAAAACGACGGCCAGTTGTTGGGAGTTTTGAGTTTT 31450/55  999-1027 Bottom (SEQ ID NO: 48) Strand GST-B2 BiotinBioAAAACCTAAAAAAAAAAAAAAAACTTCCC 314 50/55 1285-1313 DNA 3 Exon 2/3GST-14 M13 TGTAAAACGACGGCCAGTTAGTATTACGTTA 603 45/50 1317-1337 TopStrand (SEQ ID NO: 49) DNA GST-15 BiotinBioAAGTCTAACCCTAATCTAGCAACAACATA 603 45/50 1920-1892 4 Exon 4/5 GST-31M13 TGTAAAACGACGGCCAGTGTTTTGAGTATTTGTTGTC 265 55/60 2381-2410 Top Strand(SEQ ID NO: 50) DNA GST-32 BiotinBioTGTAAAACGACGGCCAGTGTTTTGATATTTGTTGTG 265 55/60 2617-2646 5 Exon 7GST-27 M13 TGTAAAACGACGGCCAGTGTTTTTAGTATATGTGG 287 50/55 3874-4132 TopStrand (SEQ ID NO: 51) DNA GST-28 BiotinBioATAGTAAAAAAACTATTTTCTAATCCTCTA 287 50/55 4161-4164

Extensions on “M13” primers for annealing of sequencing primer isunderlined. TABLE 3 Forward or Primer Reverse Primer Sequence (5′-3′)Co-ordinates CpG sites CGPS-1 F CGCGAGGTTTTCGTTGGAGTTTCGTCGTC (SEQ IDNO: 1) 1210-1238 −3 to +3 CGPS-2 F GGTTATTAGTGAGTACGCGCGGTTC (SEQ ID NO:2) 1247-1271 +4 to +8 CGPS-3 R TCCCATCCCTCCCCGAAACGCTCCG (SEQ ID NO: 8)1428-1452 +21 to +23 CGPS-4 R GAAACGCTCCGAACCCCCTAAAAACCGCTAACG (SEQ IDNO: 9) 1406-1438 +19 to +23 CGPS-5 F YGGTTTTAGGGAATTTTTTTTCGC (SEQ IDNO: 3) 894-917 −39 to −37 CGPS-6 F YGGYGYGTTAGTTYGTTGYGTATATTTC (SEQ IDNO: 4) 925-952 −36 to −31 CGPS-11 F GGGAATTTTTTTTCGCGATGTTTYGGCGC (SEQID NO: 5) 902-930 −38 to −34 CGPS-7 R CRCCCTAAAATCCCCRAAATCRCCGCG (SEQID NO: 10) 1038-1064 −23 to −27 CGPS-8 R ACCCCRACRACCRCTACACCCCRAACGTCG(SEQ ID NO: 11) 1077-1106 −16 to −21 CGPS-9 RCTCTTCTAAAAAATCCCRCRAACTCCCGCCG (SEQ ID NO: 12) 1113-1143 −12 to −15CGFS-12 R AAAACRCCCTAAAATCCCCGAAATCGCCG (SEQ ID NO: 13) 1040-1068 −23 to−26 CGPS-13 R AACTCCCRCCGACCCCAACCCCGACGACCG (SEQ ID NO: 14) 1094-1123−14 to −18 CGPS-21 F TTTTTAGGGGGTTYGGAGCGTTTC (SEQ ID NO: 6) 1415-1438+21 to +23 CGPS-22 F GGTAGGTTGYGTTTATCGC (SEQ ID NO: 7) 1473-1491 +26 to+28 CGPS-23 R AAAAATTCRAATCTCTCCGAATAAACG (SEQ ID NO: 15) 1640-1666 +36to +34 CGPS-24 R AAAAACCRAAATAAAAACCACACGACG (SEQ ID NO: 16) 1676-1703+39 to +37

TABLE 4 Assay negative Assay positive Normal subjects 10 0 Benignhyperplasia 17 1 Cancer (total) 7 17 Stage A 1 3 Stage B 3 3 Stage C 0 2Stage D 0 7 Stage not defined 3 2

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A diagnostic or prognostic assay for a disease or condition in asubject, said disease or condition characterised by abnormal methylationof cytosine at a site or sites within the glutathione-S-transferase(GST) Pi gene and/or its regulatory flanking sequences, wherein saidassay comprises the steps of; (i) isolating DNA from said subject, (ii)exposing said isolated DNA to reactants and conditions for theamplification of a target region of the GST-Pi gene and/or itsregulatory flanking sequences which includes a site or sites at whichabnormal cytosine methylation characteristic of the disease or conditionoccurs, the amplification being selective in that it only amplifies thetarget region if the said site or sites at which abnormal cytosinemethylation occurs is/are methylated, and (iii) determining the presenceof amplified DNA, wherein the amplifying step (ii) is used to amplify atarget region within the region of the GST-Pi gene and/or its regulatoryflanking sequences defined by (and inclusive of) CpG sites −43 to +55.2. An assay according to claim 1, wherein prior to the amplifying step,the isolated DNA is treated such that unmethylated cytosines areconverted to uracil or another nucleotide capable of forming a base pairwith adenine while methylated cytosines are unchanged or are convertedto a nucleotide capable of forming a base pair with guanine.
 3. As assayaccording to any one of the preceding claims, wherein the amplifyingstep involves polymerase chain reaction (PCR) amplification.
 4. An assayaccording to claim 3, wherein said PCR amplification utilises a reverseprimer including guanine at at least one site whereby, upon the reverseprimer annealing to the treated DNA, said guanine will either form abase pair with a methylated cytosine (or another nucleotide to which themethylated cytosine has been converted through said treatment) ifpresent, or will form a mismatch with uracil (or another nucleotide towhich unmethylated cytosine has been converted through said treatment).5. An assay according to claim 4, wherein said PCR amplificationutilises a forward primer including cytosine at at least one site(s)corresponding to cytosine nucleotides that are abnormally methylated inthe DNA of a subject with the disease or condition being assayed.
 6. Anassay according to claim 5, wherein the primers are of 12 to 30nucleotides in length.
 7. An assay according to claim 6, wherein theprimers are selected so as to anneal to a sequence within the targetregion that includes two to four cytosine nucleotides that areabnormally methylated in the isolated DNA of a subject with the diseaseor condition being assayed.
 8. An assay according to claim 2, whereinthe treatment of the isolated DNA involves reacting the isolated DNAwith bisulphite.
 9. As assay according to claim 8, wherein theamplifying step involves polymerase chain reaction (PCR) amplification.10. An assay according to claim 9, wherein said PCR amplificationutilises a reverse primer including guanine at at least one sitewhereby, upon the reverse primer annealing to the treated DNA, saidguanine will either form a base pair with a methylated cytosine ifpresent, or will form a mismatch with uracil.
 11. An assay according toclaim 10, wherein said PCR amplification utilises a forward primerincluding cytosine at at least one site(s) corresponding to cytosinenucleotides that are abnormally methylated in the isolated DNA of asubject with the disease or condition being assayed.
 12. An assayaccording to claim 11, wherein the primers are of 12 to 30 nucleotidesin length.
 13. An assay according to claim 12, wherein the primers areselected so as to anneal to a sequence within the target region thatincludes two to four cytosine nucleotides that are abnormally methylatedin the DNA of a subject with the disease or condition being assayed. 14.An assay according to any one of the preceding claims, wherein said DNAis isolated from cells from tissue, blood (including serum and plasma),semen, urine, lymph or bone marrow.
 15. An assay according to any one ofthe preceding claims, wherein the disease or condition to be assayed isselected from cancers.
 16. An assay according to claim 15, wherein thedisease or condition to be assayed is selected from prostate cancer,breast cancer, cervical cancer and liver cancer.
 17. An assay accordingto claim 16, wherein the disease or condition to be assayed is prostatecancer.
 18. An assay according to claim 17, wherein the amplifying stepis used to amplify a target region within the region of the GST-Pi geneand its regulatory flanking sequences defined by (and inclusive of) CpGsites −43 to +53.
 19. An assay according to claim 17, wherein theamplifying step is used to amplify a target region within the region ofthe GST-Pi gene and its regulatory flanking sequences defined by (andinclusive of) CpG sites −43 to +10.
 20. An assay according to claim 17,wherein the amplifying step is used to amplify a target region withinthe region of the GST-Pi gene and its regulatory flanking sequencesdefined by (and inclusive of) CpG sites −43 to −14.
 21. An assayaccording to claim 17, wherein the amplifying step is used to amplify atarget region within the region of the GST-Pi gene and its regulatoryflanking sequences defined by (and inclusive on CpG sites −43 to −8. 22.An assay according to any one of the preceding claims wherein the targetregion excludes any or all of the CpG sites −36, −32, −23, −20, −19 and−14.
 23. An assay according to any one of claims 5 to 21, wherein ifeither or both of the reverse or forward primers anneal to a sequencewithin the target region that includes any or all of CpG sites −36, −32,−23, −20, −19 and −14, then said PCR amplification further utilisesequivalent reverse and/or forward primers including a redundantnucleotide(s) at the position(s) within their sequence(s) correspondingto cytosine or methylated cytosine of CpG sites −36, −32, −23, −20, −19and −14.
 24. An assay according to claim 17, wherein the amplifying stepis used to amplify a target region within the region of the GST-Pi geneand its regulatory flanking sequences defined by (and inclusive of) CpGsites +9 to +53.
 25. An assay according to claim 17, wherein theamplifying step is used to amplify a target region within the region ofthe GST-Pi gene and its regulatory flanking sequences defined by (andinclusive of) CpG sites +1 to +53.
 26. An assay according to claim 17,wherein the amplifying step involves PCR amplification using primerpairs consisting of a forward and reverse printer selected from each ofthe following groups: Forward Primers CGCGAGGTTTTCGTTGGAGTTTCGTCGTC (SEQID NO: 1) CGTTATTAGTGAGTACGCGCGGTTC (SEQ ID NO: 2)YGGTTTTAGGGAATTTTTTTTCGC (SEQ ID NO: 3) YGGYGYGTTAGTTYGTTGYGTATATTTC(SEQ ID NO: 4) GGGAATTTTTTTTCGCGATGTTTYGGCGC (SEQ ID NO: 5)TTTTTAGGGGGTTYGGAGCGTTTC (SEQ ID NO: 6) GGTAGGTTGYGTTTATCGC (SEQ ID NO:7) Reverse Primers TCCCATCCCTCCCCGAAACGCTCCG (SEQ ID NO: 8)GAAACGCTCCGAACCCCCTAAAAACCGCTAACG (SEQ ID NO: 9)CRCCCTAAAATCCCCRAAATCRCCGCG (SEQ ID NO: 10)ACCCCRACRACCRCTACACCCCRAACGTCG (SEQ ID NO: 11)CTCTTCTAAAAAATCCCRCRAACTCCCGCCG (SEQ ID NO: 12)AAAACRCCCTAAAATCCCCGAAATCGCCG (SEQ ID NO: 13)AACTCCCRCCGACCCCAACCCCGACGACCG (SEQ ID NO: 14)AAAAATTCRAATCTCTCCGAATAAACG (SEQ ID NO: 15) AAAAACCRAAATAAAAACCACACGACG,(SEQ ID NO: 16)

wherein Y is C, T or a mixture thereof, and R is A, G or a mixturethereof.
 27. An assay according to claim 17, wherein the amplifying stepinvolves PCR amplification using primer pairs consisting of a forwardand reverse primer selected from each of the following groups: ForwardPrimers CGCGAGGTTTTCGTTGGAGTTTCGTCGTC (SEQ ID NO: 1)CGTTATTAGTGAGTACGCGCGGTTC (SEQ ID NO: 2) Reverse PrimersTCCCATCCCTCCCCGAAACGCTCCG (SEQ ID NO: 8)GAAACGCTCCGAACCCCCTAAAAACCGCTAACG (SEQ ID NO: 9)


28. An assay according to claim 17, wherein the amplifying step involvesPCR amplification using primer pairs consisting of a forward and reverseprimer selected from each of the following groups: Forward PrimersYGGTTTTAGGGAATTTTTTTTCGC (SEQ ID NO: 3) YGGYGYGTTAGTTYGTTGYGTATATTTC(SEQ ID NO: 4) GGGAATTTTTTTTCGCGATGTTTYGGCGC (SEQ ID NO: 5) ReversePrimers CRCCCTAAAATCCCCRAAATCRCCGCG (SEQ ID NO: 10)ACCCCRACRACCRCTACACCCCRAACGTCG (SEQ ID NO: 11)CTCTTCTAAAAAATCCCRCRAACTCCCGCCG (SEQ ID NO: 12)AAAACRCCCTAAAATCCCCGAAATCGCCG (SEQ ID NO: 13)AACTCCCRCCGACCCCAACCCCGACGACCG, (SEQ ID NO: 14)

wherein Y is C, T or a mixture thereof and R is A, G or a mixturethereof.
 29. An assay according to claim 17, wherein the amplifying stepinvolves PCR amplification using primer pairs consisting of a forwardand reverse primer selected from each of the following groups: ForwardPrimers TTTTTAGGGGGTTYGGAGCGTTTC (SEQ ID NO: 6) GGTAGGTTGYGTTTATCGC (SEQID NO: 7) Reverse Primers AAAAATTCRAATCTCTCCGAATAAACG (SEQ ID NO: 15)AAAAACCRAAATAAAAACCACACGACG, (SEQ ID NO: 16)

wherein Y is C, T or a mixture thereof, and R is A, G or a mixturethereof.
 30. An assay according to claim 16, wherein the disease orcondition to be assayed is liver cancer.
 31. An assay according to claim30, wherein the amplifying step is used to amplify a target regionwithin the region of the GST-Pi gene and its regulatory flankingsequences defined by (and inclusive of) CpG sites −43 to −14.
 32. Anassay according to claim 31, wherein the target region excludes any orall of the CpG sites −36, −32, −23, −20, −19, and −14.
 33. An assayaccording to claim 30, wherein if either or both of the reverse orforward primers anneal to a sequence within the target region thatincludes any or all of CpG sites −36, −32, −23, −20, −19 and −14, thensaid PCR amplification further utilises equivalent reverse and/orforward primers including a redundant nucleotide(s) at the position(s)within their sequence(s) corresponding to cytosine or methylatedcytosine of CpG sites −36, −32, −23, −20, −19 and −14.
 34. An assayaccording to claim 30, wherein the amplifying step is used to amplify atarget region within the region of the GST-Pi gene and its regulatoryflanking sequences defined by (and inclusive of) CpG sites +9 to +53.35. A diagnostic or prognostic assay for a disease or condition in asubject said disease or condition characterised by abnormal methylationof cytosine at a site or sites within the glutathione-S-transferase(GST) Pi gene and/or its regulatory flanking sequences, wherein saidassay comprises the steps of; (i) isolating DNA from said subject, and(ii) determining the presence of abnormal methylation of cytosine at asite or sites within the region of the GST-Pi gene and/or its regulatoryflanking sequences defined by (and inclusive of) CpG sites −43 to +55.36. An assay according to claim 35, wherein the region of the GST-Pigene and its regulatory flanking sequences within which the presence ofmethylated cytosine(s) at a site or sites is determined is selected fromthe regions defined by (and inclusive of) CpG sites −43 to +53, −43 to+10, −43 to −14, +9 to +53 and +1 to +53.
 37. An assay according toclaim 35 or 36, wherein the said region of the GST-Pi gene and itsregulatory flanking sequences excludes any or all of the CpG sites −36,−32, −23, −20, −19 and −14.
 38. An assay according to claim 36, whereinthe region of the GST-Pi gene and its regulatory flanking sequenceswithin which the presence of methylated cytosine(s) at a site or sitesis determined is the region defined by (and inclusive of) CpG sites +9to +53.
 39. An assay according to claim 36, wherein the region of theGST-Pi gene and its regulatory flanking sequences within which thepresence of methylated cytosine(s) at a site or sites is determined isthe region defined by (and inclusive of) CpG sites +1 to +53.
 40. Anassay according to any one of claims 35 to 39, wherein prior to thedetermination step, the isolated DNA is treated such that unmethylatedcytosines are converted to uracil or another nucleotide capable offorming a base pair with adenine while methylated cytosines areunchanged or are converted to a nucleotide capable of forming a basepair with guanine.
 41. An assay according to claim 40, wherein thetreatment of the isolated DNA involves reacting the isolated DNA withbisulphite.
 42. An assay according to any one of claims 35 to 41,wherein the determination step involves selective hybridisation ofoligonucleotide/polynucleotide/peptide-nucleic acid (PNA) probe(s). 43.An assay according to claim 42, wherein if the probe(s) hybridise to asequence within the target region that includes any or all of CpG sites−36, −32, −23, −20, −19 and −14, then said selective hybridisationsfurther utilises equivalent probe(s) including a redundant nucleotide(s)at the position(s) within their sequence(s) corresponding to cytosine ormethylated cytosine of CpG sites −36, −32, −23, −20, −19 and −14.
 44. Anassay according to any one of claims 35 to 43, wherein said DNA isisolated from cells from tissue, blood (including serum and plasma),semen, urine, lymph or bone marrow.
 45. An assay according to any one ofclaims 35 to 43, wherein the disease or condition to be assayed isselected from cancers.
 46. An assay according to claim 45, wherein thedisease or condition to be assayed is selected from prostate cancer,breast cancer, cervical cancer and liver cancer.
 47. An assay accordingto claim 46, wherein the disease or condition to be assayed is prostatecancer.
 48. An assay according to claim 46, wherein the disease orcondition to be assayed is liver cancer.
 49. A primer or probecomprising a nucleotide sequence selected from the group consisting of:CGCGAGGTTTTCGTTGGAGTTTCGTCGTC (SEQ ID NO: 1) CGTTATTAGTGAGTACGCGCGGTTC(SEQ ID NO: 2) YGGTTTTAGGGAATTTTTTTTCGC (SEQ ID NO: 3)YGGYGYGTTAGTTYGTTGYGTATATTTC (SEQ ID NO: 4)GGGAATTTTTTTTCGCGATGTTTYGGCGC (SEQ ID NO: 5) TTTTTAGGGGGTTYGGAGCGTTTC(SEQ ID NO: 6) GGTAGGTTGYGTTTATCGC (SEQ ID NO: 7)AAAAATTCRAATCTCTCCGAATAAACG (SEQ ID NO: 8) AAAAACCRAAATAAAAACCACACGACG(SEQ ID NO: 9) TCCCATCCCTCCCCGAAACGCTCCG (SEQ ID NO: 10)GAAACGCTCCGAACCCCCTAAAAACCGCTAACG (SEQ ID NO: 11)CRCCCTAAAATCCCCRAAATCRCCGCG (SEQ ID NO: 12)ACCCCRACRACCRCTACACCCCRAACGTCG (SEQ ID NO: 13)CTCTTCTAAAAAATCCCRCRAACTCCCGCCG (SEQ ID NO: 14)AAAACRCCCTAAAATCCCCGAAATCGCCG (SEQ ID NO: 15)AACTCCCRCCGACCCCAACCCCGACGACCG, (SEQ ID NO: 16)

wherein Y is a mixture of C and T, and R is a mixture of A and G.
 50. Aprobe comprising a nucleotide sequence selected from the groupconsisting of: AAACCTAAAAAATAAACAAACAA (SEQ ID NO: 17)GGGCCTAGGGATAAACAGACAG (SEQ ID NO: 18) CCTTTCCCTCTTTCCCARRTCCCCA (SEQ IDNO: 19) TTTGGTATTTTTTTTCGGGTTTTAG (SEQ ID NO: 20)CTTGGCATCCTCCCCCGGGCTCCAG (SEQ ID NO: 21) GGYAGGGAAGGGAGGYAGGGGYTGGG.(SEQ ID NO: 22)